Mr Toad, responding as just a dumb engineer
, interesting that Beoing have tried it. I would imagine that the biggest problem is scaling up the blades, so what in an attack heli would be 15% hinge offset might go down to 8% in CH-47. I imagine the vibration is caused by the onset of retreating blade stall, since the vortex shedding generates useful lift for each cycle in heli cruise - so all helis will do it to some extent. To get the most benefit would require additional props to generate cruise thrust.
Dave, i suspect the real reason interleavers have never made either service or market is the width of the aircraft on or near the ground. There may be advantages once airborn, but parked up those rotors are just an annoying waste of space that take up hangar volume or interfere with ground ops. Don't forget the whole point of a heli is to operate away from nice long runways with neatly painted ground boxes.
Mart